Testing high‐resolution nitrous oxide emission estimates against observations using an atmospheric transport model

Abstract

Global monthly estimates of N2O emissions were used to prescribe a three‐dimensional atmospheric transport model. The simulated N2O surface concentrations in the northern hemisphere (NH) are in general agreement with atmospheric observations, about 1 ppb higher than in the southern hemisphere (SH). The results suggest that N2O concentrations over strong source regions in continental interiors are much higher than those over oceans. Simulated N2O concentrations in the NH vary strongly with the season, while the measured concentrations oscillate strongly without seasonality. The modelled results for the SH show much less seasonal variation, which is more consistent with atmospheric measurement data. Most atmospheric N2O monitoring stations are not well situated for verifying the simulated seasonality in atmospheric N2O. There is only one continental site. In addition, atmospheric N2O observations from different studies are sometimes contradictory. The difference between model results and observations may be the result of local scale pulses of N2O acting on a much shorter timescale than the time step of 1 month of the emission inventory. Such N2O pulses may cause oscillations of the N2O concentration at the monitoring sites which dominate the large‐scale seasonality. It is also possible that source and sink processes other than those included in this study are operating. The transport model does not include a description of the downward stratosphere‐troposphere flux of N2O which is greater in the NH than in the SH. The emission inventory does not account for soil N2O consumption in N‐limited temperate ecosystems, and N2O emissions during autumn, thaw periods, and from snow covered soils. These potential errors and possible underestimation of N2O emissions from combustion sources may exaggerate the simulated seasonal trends.